Polysaccharides, in particular galactomannans such as guar, have a variety of uses. Guar in the form of gum is used primarily in food and personal care products for its thickening property. The gum has five to eight times the thickening power of starch. Guar gum is also used as a fracturing aid in oil production.
Guar gum is the mucilage found in the seed of the leguminous plant Cyamopsis tetragonolobus. The seeds are composed of a pair of tough non-brittle endosperm sections, hereinafter referred to as guar splits. Guar splits contain guar gum but are tough and extremely difficult to grind into a powder form for recovery of the gum. After processing, native guar gum is obtained in the form of a yellow powder and has a molecular weight of between about 2,000,000 Daltons and 5,000,000 Daltons.
In certain applications, such as in food products, cosmetics, and shampoos, it would be desirable to use a polysaccharide, in particular a galactomannan such as guar gum, that is modified by grafting thereto a functional group such as a vinyl monomer, or other material. It would also be desirable that the grafted polysaccharide, galactomannan or guar gum be dispersible and/or soluble in water and have a molecular weight lower than the ungrafted polysaccharide, galactomannan or guar.
It was reported that guar was grafted with acrylamide in the presence of Cerium (IV). Deshmukh, S. R.; Singh, R. P. J. Appl. Polym. Sci. (1987) 33, 1963. Guar was grafted with acrylonitrite under gamma radiation to yield a water superabsorbent. Lokhande, H. T. et al. J. AppI. Polym. Sci. (1992), 45, 2031-20-36. The use of an initiator such as cerium (IV) is not industrially feasible due to the toxicity and the cost. Although the gamma irradiation grafting polymerization provides a way to produce the grafted guar, the irradiation itself requires expensive containment and a radioactive source.
It was reported in Romanian Patent 66503 that cellulositic products with improved properties (especially resistance to microorganisms) were prepared by grafting fibrous cellulositic materials (e.g. cotton fabric) with monomers (e.g. methylmethacrylate, vinyl chloride or vinylidone chloride at 10-25° C. with accelerated electrons of 500-3000 MeV at 108-109 rads and a total dose of 1-3 Mrads and a current strength of 20-25 A. The fibrous cellulose materials were given a preliminary treatment with NaOH at 90° C. for 60 minutes.
High energy electron beams have been used to graft vinyl monomers to polysaccharides, such as starch and cellulose. Olivier, A. et al. Biomacromolecules (2001), 2, 1260-1266; Ruckert, D. et al. J. Appl. Polym. Sci. (1999), 73 409-417; Yamagishi, H. et al. J. Membr. Sci. (1993), 85, 71-81; Ratzsch, M. et al. Acta Polym. Sci. (1999), 41, 620-7. There are numerous other articles describing how to graft vinyl monomers to polysaccharides, mainly cellulose and starch, in order to make plastic composite materials, and/or to give a property to the solid surfaces, such as fiber or membrane. Insofar as is known, however, it has not previously been proposed to modify water dispersible and/or soluble polysaccharides such as galactomannans or water dispersible and/or soluble cellulose derivatives with vinyl monomers with the intention of producing new products that can be used preferably in liquid compositions. Moreover, none of the graft polysaccharides previously reported was described as having a molecular weight lower than the original polysaccharides, while controlling the molecular weight during the grafting.